1. Field of the Invention
The present invention relates to an ion source device.
2. Description of the Related Art
An ion source device is used for the ion implantation apparatus which is intended to implant impurity ions into the semiconductor wafer. Most of the ion source devices are of such type that voltage is added between a filament in an ion source chamber and an anode electrode, that a predetermined gas introduced into the ion source chamber is made plasma, and that desired ions are extracted from the plasma and then used for some purposes. The ion source device of the Freeman type can be cited as an example.
An ion source device of the electron beam exciting type is disclosed in Published Unexamined Japanese Patent Application No. 62-278736. In the case of this device, voltage is applied between the filament and the anode electrode to generate first plasma from the predetermined gas. Electrons are then extracted from the first plasma and introduced into an ion generating chamber. The electrons are radiated to an ion generating gas, which has been introduced into the ion generating chamber, to thereby generate second plasma. Ions in the second plasma are then drawn out-side through a slit of the ion generating chamber.
The ion source device of this electron beam exciting type is advantageous in that high density ions are available although energy used is low.
Components by which the ion source device is made are worn away by the sputtering and etching with ions in plasma. In addition, particles scattered from these worn-away parts of the components adhere, as sub-products. To the components and they are thus deposited on the components. This makes it necessary to exchange these components with new ones or add periodic maintenances such as cleaning to them.
When a high corrosion-proof gas is used as raw gas, it becomes more remarkable that the components are worn away and that the sub-products are deposited on them. When the ion generating chamber is made of molybdenum and the raw gas used is BF.sub.3 (boron trifluoride) in the case of the ion source device of the electrons beam exciting type, insulating matters such as molybdenum fluoride adhere to the surface of an ion attraction electrode. Films of these matters are thus formed on the electrode to thereby make it impossible to obtain predetermined attraction voltage. In addition, the electric field-face becomes not uniform to thereby make it impossible to obtain the capacity of the predetermined ion source to an extent intended.
Ions generated are passed through the slit of the ion generating chamber. Components around the slit are thus sputtered and etched by the ions and worn away. The ion generating chamber provided with this ion emitting slit must be periodically maintained or exchanged with a new one if necessary.
In order to exchange only those components, which have been severely worn away, with new ones during the maintaining process, it has been proposed that the ion source device is assembled by plural detachable components and that these components are fixed as a unit by connecting rods.
The ion source device made in this manner is heated to a temperature higher than 800.degree. C. when ions are to be generated. It is therefore thermally and repeatedly expanded and contracted so that its components can be distorted and split not to generate predetermined and stable ions. In addition, screws for fixing the connecting rods are baked, thereby making it difficult to dismantle the components or breaking them.